Electric immersion heater



Se@ i2? W. H. EULEWT 1291729495 l ELECTRIC. IMMERSION HEATER Filed Sept.12, EEES 2 sheets-sheet l Umm? Hem BELEK epia E29 39553, W, @ULPTT293729495 ELECTRIC IMMERSION HEATER Filed Sept. l2, 1938 2 Sheets-Shed 2Patented Sept. 12, 1939 UNITED STATES PATENT OFFICE ApplicationSeptember 12, 1938, Serial No. 229,623 In Great Britain December 3, 19368 Claims.

'I'nis `invention relates to electric immersion heaters of the kindcomp-rising a tubular metal casing of 'loop form, this looped casingenclosing aresistance Vwinding and having its ends mounted in a plugwhich is adapted to be secured in an opening in the wall rof a vesselcontaining the liquid to be heated.

In connection with immersion heaters, it is a common practice to providea safety deviceV whereby the current is automatically cut off when acertain temperature is reached, The object of this is to ensure thatneither the heater nor the vessel itself will be damaged in the event ofthe heater being forgotten or neglected until all the liquid in thekettle or other vessel has been evaporated.

The object of the present invention is to effect certain improvements inheaters of the kind referred to.

Referring to the drawings- Figure 1 is a part-sectional side elevationof a vessel provided with an immersion heater in accordance with thepresent invention.

Figure 2 is a part-sectional plan View of same.

Figure 3 is a perspective View of the heater.

Figures 4 and 5 are respectively a part-sectional side elevation andplan view of the heater to an enlarged scale.

Figure 6 is a View corresponding to part of Figure 5 but showing amodified construction.

Figure '7 is a View corresponding to Figure l showing a furthermodification.

In the construction illustrated, the immersion heater includes aresistance wire I'I which is A wound upon a mica strip or other suitablesupport, the latter being then inserted into a flat section seamlesstubular casing Ill. This casing is subsequently bent into loop form andhas a flat section whose major dimension is perpendicular to the planeof the loop.

It Will be seen that the loop aforesaid is of incomplete circular shape,the terminal portions II of the casing I0 being turned outwardly intosubstantially parallel relationship and secured to the inner end of ahollow metal plug I2 This plug I2 is adapted for insertion in an openingI3 in the wall of a kettle or other vessel I4, and is provided with ashoulder I5 which abuts the inner face of such wall. The body of theplug I2 may be screw threaded to receive a nut I6 which engages theoutside of the vessel I.

'Ihe ends of the resistance winding Il are connected, directly orotherwise, to terminal pins I8 carried by an insulating block I9 in theouter end of the plug I2. The plug I2 forms one (Cl. 21S-38) part of acoupling, the movable part of which is indicated at 2G and carriessockets for engagement with the pins I9 in known manner.

The safety device associated with the heater is conveniently constructedas described in Let- 5 ters Patent No. 1,887,082, issued to me onNovember 8, 1932, in which case it comprises a stationary square sectionpin 2l and a catch member 22 accommodated in a groove in said pin, adepending lug 23 at one end of the member 22 10 being journalled in adiametral hole in the pin 2l and normally held against rotation by meansof fusible metal, such as solder. A thin metal sleeve 24 fits over thepin 2i, and a compression spring 25 is mounted between the two members,15 the sleeve 24 being held in position by the engagement of a catch 26on the member 22 with a projection 2l on one side of a slot 28 in thesleeve 24.

When a predetermined temperature is reached, 20 the fusible metal meltsand leaves the member 22 free to rotate, so that the sleeve 2G can slidealong the pin 2i under the action of the spring 25, the projection 2slipping past the catch 25. This movement of the sleeve 24 is made useof to force 25 the movable part 2l) of the coupling oif the terminalpins I8 and so break the circuit.

At the end of its movement the sleeve 2t returns the member Z2 to itsoriginal position by engagement of a second projection 29 in the slot 30y 28 with the catch 26, the safety device being reset after the fusiblemetal has solidified by pushing back the sleeve 24 against the spring25.

The safety device is mounted upon, and in direct metallic connectionwith, the exterior of 35 the tubular casing Ii! of the heater at aposition remote from the plug I2 The above arrangement ensures that theoperation of the safety device is not affected by the coating of limeand other deposit which the 40 looped casing inevitably acquires afterprolonged use of the heater in hard water. It is a serious disadvantageof certain prior constructions of immersion heater of the kind to whichthe present invention relates, that the safety device is lo- 45 cated inor adjacent the contact-carrying plug, because this deposit is alwaysparticularly heavy where the two ends of the looped casing are closetogether. If the level of the water in the vessel is allowed to sinkbelow the lowest part of the 50 heater, these closely-spaced parts ofthe casing (and hence the safety device) tend to remain cooler than therest of the heater owing to the moisture which the deposit thereon hasabsorbed, and it has frequently been found with the prior constructionsin question, that the safety device operates too late to save theresistance winding of the heater from being burned out.

To protect it from the liquid Within the vessel I 4, the safety devicemay be enclosed within a tube 30 which extends diametrically across theloop of the heater casing I0, the end of this tube being soldered orotherwise secured to the casing I0 and plug I2 respectively. With asafety device of the kind illustrated, the outer end of the tube 30 maycontain a hollow plug 3l into which the pin 2l of the safety device isscrewed and which is itself soldered to the inner wall of th casing I0.

The sleeve 2li or other movable part of the safety device acts upon apush-rod 32 Which eX- tends axially through the tube 30 and Whose freeend is slidably supported in a central hole 33 in the insulating blockI9 carried by the bush I2. When the movable part 20 of the coupling isin position on the terminal pins I8, its face abuts the end oi thepush-rod 32. Endwise movement of the latter thus causes the parts of thecoupling to be separated, so that the circuit is broken.

The push-rod 32 may be soldered to the sleeve 2li at 36, and it may beprovided with a collar 35 which acts as a stop to limit its movementwith the sleeve 2li.

As already mentioned the deposit upon the irnmersion heater is found tobe greatest when the two ends Il of the casing I8 are attached to thebush l2, the space between the ends II tending to become choked withdeposit so that as a consequence this part of the heater becomesinecient.

With the object .of overcoming this difficulty, the terminal portions IIof the heater casing III1 instead of being bent into substantiallyparallel relationship, may be brought into alignment as shown in Figure6 and inserted between a clamping plate Sii and the iiange l5 of thebush I2, so that the loop form of the heater casing I0 becomespractically circular and does not provide any very restricted space tobe choked with deposit. Y

The arrangement of the heater casing may be such as to ensure that, whenthe level of liquid in the vessel Ill sinks, the part of the heater atwhich the safety device is located will become uncovered (and thussubject to overheating) before the rest of the heater.

In the construction shown in Figure '7, the desired effect is obtainedby mounting the looped casing lil in the vessel I4 with the plane of theloop somewhat inclined to the horizontal, the central portion of thecasing being at a higher level than its ends. The safety device isconnected to the central portion aforesaid and thus operates, whenoverheating occurs, in s'uicient time to prevent damage to theresistance winding of the heater.

What I claim then is:

l. In combination, a vessel for holding liquid, an electric heatermounted within said vessel and adapted for immersion in said liquid,said heater comprising a tubular metal casing enclosing a V'resistancewinding and bent into loop form, said loop being disposed transverse tosaid vessel and spaced above the base thereof, a plug adapted to besecured in an opening in the wall of said vessel and having the ends ofsaid looped casing secured therein, a'spring-loaded member' eiectivewhen released to cut off the current through said heater, andheat-responsive means adapted to hold said spring-loaded member ina'retracted position against the action of said spring and automaticallyto release said spring-loaded member on attainment of a predeterminedtemperature, said heat-responsive means being mounted exteriorly of saidlooped casing and in direct metallic connection with the same at aposition remote from the ends thereof.

2. In combination, a vessel for holding liquid, an electric heatermounted within said vessel and adapted for immersion in said liquid,saidheater comprising a tubular metalv casing enclosing a resistance windingand bent into loop form, said loop being disposed transverse to saidvessel and spaced above the base thereof, a plug adapted to be securedink an opening in the wall of said vessel and having the ends of saidlooped casing secured therein, contact members carried by said plug andconnected to the ends of said resistance winding, said plug constitutingone of the two parts of an electrical coupling through which current istaken to said heater, a springloaded member eiective when released toseparate the parts of said coupling, and heat-responsive means adaptedto hold said spring-loaded member in a retracted position against vtheaction of said spring and automatically to release said spring-loadedmember on attainment of a predetermined temperature, saidheat-responsive means being mounted exteriorly of said looped casing andin direct metallic connection with the same at a position remote fromthe ends thereof.

3. In combination, a vessel for holding liquid, an electric heatermounted within said vessel and adapted for immersionk in said liquid,said heater comprising a tubular metal casing enclosing a resistancewinding and bent into loop form, said loop being disposedtransverse tosaid vessel and spaced above the base'thereof, a plug adapted to besecured in an opening in the Wall of said vessel and having the ends ofsaid looped casing secured therein, contact members carriedby said plugand connected to the ends of said resistance winding, said plugconstituting one of the two parts of an electrical coupling throughwhich current is taken to said heater, a spring-loaded plunger extendingthrough said plug and adapted to engage the other of said couplingmembers, and heat-responsive means adapted to hold said springloadedplunger in a retracted position allowing connection together of saidcoupling members, said heat-responsive means being mounted in directmetallic connection with the exterior of said looped casing at aposition remote from the ends thereof and being adapted on attainment ofa predetermined temperature automatically to release said plunger,whereupon the latter operates to separate said coupling members.

4. In combination, a vessel for holding liquid,v

an electric heater mounted within said vess'eland adapted for immersionin said' liquid, said heater comprising a tubular lmetal casingenclosing a resistance winding and bent into the shapeof a substantiallycircular loop disposed transversely of said vessel in proximity to thevbase thereof, a plug adapted to be secured in an opening in the wall ofsaid vessel, the ends of said looped casing extending side by side inclosely spaced relationship and being secured in said plug, aspring-loaded member eiectivewhen released`to cut oi the current throughsaid heater and heat'-v responsive means adapted to hold saidspringloaded member in a retracted position against the action of saidspring and automatically to releasesaid spring-loaded member'onattainment 75 of a predetermined temperature, said heat-responsive meansbeing mounted upon and in direct metallic connection with said casing ata position on the inside of said loop substantially opposite to saidplug.

5. n combination, a vessel for holding liquid, an electric heatermounted within said vessel and adapted for immersion in said liquid,said heater comprising a tubular metal casing enclosing a resistanceelement and bent into loop form, said loop being disposed in a planetrans- Verse to said vessel and tilted with reference to the surface ofliquid in said vessel when the latter is in its normal position, a plugadapted to be secured in an opening in the wall of said Vessel andhaving the ends of said looped casing secured therein, said casing endsbeing spaced above the base of said vessel and disposed at a lower levelthan the central portion of said casing, a spring-loaded membereffective when released to cut oi the current through said heater, andheat-responsive means adapted to hold said spring-loaded member in aretracted position against the action oi said spring and automaticallyto release said spring-loaded member on attainment of a predeterminedtemperature, said heat-responsive means being mounted upon and in directmetallic connection with the central portion of said casing.

6. In combination, a vessel for holding liquid, an electric heatermounted within said Vessel and adapted for immersion in said liquid,said heater comprising a tubular metal casing enclosing a resistancewinding and bent into loop form, said loop being disposed transverse tosaid Vessel and spaced above the base thereof, a plug adapted to besecured in an opening in the wall of said vessel and having the ends ofsaid looped casing secured therein, contact members carried by said plugand connected to the ends of said resistance winding, said plugconstituting one of the two parts of an electrical coupling throughwhich current is taken to said heater, a spring-loaded plunger extendingthrough said plug and adapted to engage the other of said couplingmembers, heat-responsive means adapted to hold said spring-loadedplunger in a retracted position allowing connection together or" saidcoupling members, said heat-responsive means being mounted in directmetallic connection with said casing at a position on the inside of saidloop substantially opposite to said plug and being adapted on attainmentof a predetermined temperature automatically to release said plunger,whereupon the latter operates to separate said coupling mem` bers, and ahollow member extending across said loop from said plug so as to enclosesaid plunger and heat-responsive means in a fluid-tight manner.

7. In combination, a vessel for holding liquid, an electric heatermounted within said Vessel and adapted for immersion in said liquid,said heater comprising a tubular metal casing enclosing a resistancewinding and bent into the shape oi a substantially circular loopdisposed transversely of said vessel in proximity to the base thereof, aplug adapted to be secured in an opening in the wall of said vessel, theends of said looped casing extending side side in closely spacedrelationship and being secured in said plug, contact members carried bysaid plug and connected to the ends oi said resistance winding, saidplug constituting one of the two parts of an electrical coupling throughwhich current is taken to said heater, a spring-loaded plunger extendingthrough said plug and adapted to engage the other of said couplingmembers, heat-responsive means adapted to hold said spring-loadedplunger in a retracted position allowing connection together of saidcoupling members, said heat-responsive means being mounted in directmetallic connection with said casing at a position on the inside of saidloop substantially opposite to said plug and being adapted on attainmentof a predetermined temperature automatically to release said plunger,whereupon the latter oper- C ates to separate said coupling members, anda 8. 1n combination, a vessel for holding liquid,

an electric heater mounted within said Vessel and adapted for immersionin said liquid, said heater comprising a tubular metal casing enclosinga resistance winding and bent into the shape of a substantially circularloop disposed transversely of said vessel in proximity to the basethereof, a plug adapted to be secured in an opening in the wall of saidvessel, the ends of said looped casing being aligned with one another incloselyspaced relationship, a plate clamping said casing ends to theinner face of said plug, contact members carried by said plug andconnected to the ends of said resistance winding, said plug constitutingone of the two parts of an electrical coupling through which current istaken to said heater, a spring-loaded plunger extending through saidclamping plate and said plug and adapted to engage the other of saidcoupling members, and heat-responsive means adapted to hold saidspring-loaded plunger in a retracted position allowing connectiontogether of said coupling members, said heat-responsive means beingmounted in direct metallic connection with the exterior of said loopedcasing at a position remote from the ends thereof and being adapted onattainment of a predetermined temperature automatically to release saidplunger, whereupon the latter operates to separate said couplingmembers.

WALTER H. BULPITT.

